A lime causticization regeneration process for deodorizing absorption liquid of printing and dyeing wastewater

Abstract

The application provides a lime causticization regeneration process of printing and dyeing wastewater deodorization absorption liquid, which comprises the following steps: pretreating the printing and dyeing wastewater deodorization absorption liquid to be regenerated, removing suspended solids and mechanical impurities, and obtaining clear waste lye; reacting the pretreated clear waste lye with calcium hydroxide in a causticization reactor, converting sodium carbonate into calcium carbonate precipitate, and converting sulfide into calcium sulfide; performing solid-liquid separation on the mixed liquid after the reaction is completed; the solid phase obtained by the separation is mainly calcium carbonate and contains calcium sulfide, and the solid phase is used for elemental sulfur recovery or as a building material raw material; the liquid phase obtained by the separation is sodium hydroxide regeneration liquid, which is reused in a printing and dyeing wastewater deodorization system or reused after being adjusted in concentration. The application regenerates NaOH by causticization reaction of waste lye, reduces the cost of reagents and energy consumption, and converts Na2CO3 and Na2S in the waste lye into reusable CaS precipitate, which creates conditions for sulfur resource recovery.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection technology, and in particular relates to a lime causticization regeneration process for deodorizing absorbent liquid in dyeing and printing wastewater. Background Technology

[0002] Chemical absorption is one of the mainstream technologies for industrial waste gas treatment, widely used in the treatment of high-concentration odorous gases in industries such as petrochemicals, wastewater treatment, and landfill. This method utilizes alkaline absorbents such as NaOH and Na2CO3 to chemically react with acidic pollutants such as H2S, organic sulfides, and CO2, achieving highly efficient removal of pollutants.

[0003] Taking wastewater treatment in a dyeing and printing industrial park as an example, the exhaust gas generated by the hydrolysis acidification tank contains a design concentration of 1000 mg / m³. 3 High concentrations of H2S and 1%–1.5% CO2 are typically treated using an 8% (w / w) NaOH solution as the absorbent. A typical process flow is a three-stage treatment: a front-end alkaline scrubbing tower, a biological filter, and a back-end alkaline scrubbing tower. After absorbing H2S and CO2, the absorbent's main components are converted to Na2S, Na2CO3, and a small amount of unreacted NaOH. When the pH drops below 12, the absorption efficiency decreases significantly, requiring waste liquid discharge and replenishment with fresh NaOH. This waste liquid is classified as hazardous waste (HW35), with treatment costs as high as 2000-3000 RMB / ton. While absorbing H2S, the NaOH absorbent also co-absorbs CO2 to form Na2CO3. The accumulation of Na2CO3 lowers the solution pH, weakening its ability to absorb H2S and leading to frequent absorbent failure. To address absorbent failure, the usual approach is to replace the absorbent; however, this is costly. Therefore, chemically treating the failed absorbent to restore its absorption capacity has become an alternative solution. The existing technology for converting Na₂CO₃ to NaOH typically employs the lime causticization method. While this method is a traditional technique used in the alkali production industry, it presents several challenges when applied to the reuse of exhausted absorbent solutions. Traditional causticization methods typically require temperatures of 60-90℃, resulting in high energy consumption; they primarily target Na₂CO₃ and are insufficient for handling complex systems containing Na₂S; and they often involve excessive lime addition, leading to an increase in Ca²⁺ in the regenerated solution. 2+ Excessive residue can lead to scaling during reuse. Furthermore, significant amounts of valuable components such as Na₂S and Na₂CO₃ are not recovered from the exhausted absorption waste liquid. For example, a large petrochemical industrial park produces 30,000 tons of alkaline absorption waste liquid annually, containing sulfur resources equivalent to 5,000 tons of sulfur. Direct disposal of this waste results in resource waste and increased carbon emissions.

[0004] Therefore, developing an efficient, economical, and industrially scalable regeneration process for mixed alkaline waste liquid containing sulfur and carbon, and achieving both volume reduction and resource utilization of the absorbent, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a lime causticization regeneration process for deodorizing absorbent liquid in dyeing and printing wastewater, so as to solve the technical problems existing in the background art.

[0006] The technical solution adopted in this invention is as follows: a lime causticizing regeneration process for deodorizing absorbent liquid in dyeing and printing wastewater, comprising the following steps: (1) The deodorization absorption liquid of the dyeing and printing wastewater to be regenerated is pretreated to remove suspended solids and mechanical impurities, and a clear waste alkali liquid is obtained. (2) The pretreated clarified waste alkaline solution is reacted with calcium hydroxide in a causticizing reactor to convert sodium carbonate into calcium carbonate precipitate and sulfide into calcium sulfide. (3) The mixture after the reaction in step (2) is subjected to solid-liquid separation; the solid phase obtained is mainly calcium carbonate and contains calcium sulfide. The solid phase is used for elemental sulfur recovery or as a building material raw material; the liquid phase obtained is sodium hydroxide regenerated liquid, which is reused in the dyeing and printing wastewater deodorization system or reused after adjusting the concentration.

[0007] More preferably, the above-mentioned deodorizing absorbent for dyeing and printing wastewater to be regenerated is a saturated absorbent obtained by absorbing waste gas containing H2S and CO2 with NaOH solution.

[0008] More preferably, the above-mentioned saturated absorbent is in the form of S 2- The calculated Na2S concentration is 130-170 g / L, with CO3... 2- The calculated Na2CO3 concentration is 80-130 g / L, with OH... - The calculated NaOH concentration is 10-30 g / L, and the pH value is 12.5-14.0.

[0009] More preferably, the above pretreatment steps include: using a bag filter or centrifugal filter to perform solid-liquid separation on the deodorizing absorbent of the dyeing and printing wastewater to be regenerated, with the filtration accuracy controlled below 100 μm; and during the pretreatment process, monitoring the pH value of the waste alkali solution in real time using a pH meter.

[0010] More preferably, in step (2) above, when the clarified waste alkaline solution and calcium hydroxide react in the causticizing reactor, the reaction temperature is controlled at 15-35℃, the amount of calcium hydroxide added is controlled at 100%-110% of the theoretical amount of lime causticizing reaction, and the reaction time is controlled at 60-90 min.

[0011] In a further preferred embodiment, when the clarified waste alkaline solution and calcium hydroxide react in the causticizing reactor in step (2) above, the reaction temperature is controlled at 25±2℃, the amount of calcium hydroxide added is controlled at 100% of the theoretical amount of lime causticizing reaction, and the reaction time is controlled at 90 min.

[0012] In a further preferred embodiment, when the clarified waste alkaline solution and calcium hydroxide react in the causticizing reactor, the clarified waste alkaline solution is added dropwise to the calcium hydroxide base solution, with calcium hydroxide as the base solution.

[0013] More preferably, the above-mentioned addition adopts a reverse addition or co-current addition method, and the addition time of the clarified waste alkali liquid is controlled to be within 1 / 3 of the total reaction time.

[0014] More preferably, the causticizing reactor is a batch stirred reactor or a continuous reactor; when the causticizing reactor is a batch stirred reactor, the reactor is equipped with a jacketed temperature control system, and the pH value is monitored online during the reaction; when the causticizing reactor is a continuous reactor, it is a three-stage series stirred reactor or tubular reactor, and the residence time of the material in a single-stage reactor is controlled to be 20-40 min.

[0015] In a further preferred embodiment, the above process also includes an automated control step: based on real-time monitoring of the pH value and conductivity of the waste alkaline solution using a pH meter and conductivity meter, and by using the waste alkaline solution composition data measured by an online ion concentration analyzer, the theoretical requirement for calcium hydroxide is automatically calculated, and then precisely added using a variable frequency metering pump.

[0016] Compared with existing technologies, the beneficial effects of this invention are as follows: The lime causticization regeneration process of the deodorizing absorbent liquid for dyeing and printing wastewater of this invention reuses the regenerated NaOH in the front-end deodorization system, which can replace 14-15% of the fresh NaOH dosage, significantly reducing reagent costs and energy consumption. This process can achieve near-zero discharge of the absorbent liquid, reducing waste liquid generation by more than 90%, and the Ca content in the regenerated liquid is reduced. 2+ The residual concentration is strictly controlled below 35 mg / L, effectively avoiding the risk of equipment scaling during reuse and ensuring the long-term stable operation of the deodorization system. In addition, the regeneration process converts Na2CO3 and Na2S in the waste liquid into reusable NaOH, and creates conditions for sulfur resource recovery through the separated CaS precipitation. This not only reduces carbon emissions in the production of NaOH and the incineration of waste liquid, but also successfully builds a circular economy model of "treating waste with waste", realizing the resource utilization of all components of pollutants.

[0017] This invention reveals that for mixed waste liquids containing Na₂S and Na₂CO₃, a highly efficient lime causticization reaction can be achieved at ambient temperatures of 15-35℃, with a NaOH regeneration rate exceeding 75% and a CO₃²⁻ regeneration rate of over 75%. 2-The removal rate can reach over 97%. This is significantly different from the causticization process requiring 60-90℃ in traditional alkali production, greatly reducing energy costs. This invention determines the lime dosage through theoretical calculations and strictly controls the dosage to 100%-110% of the theoretical amount, preferably using an equimolar ratio. This precise control avoids the Ca2+ caused by excessive lime addition in traditional methods. 2+ To address residue issues and ensure that no CaCO3 or CaS scale forms in the alkaline washing tower during regeneration solution reuse, this invention has determined the optimal reaction time to be 90 minutes through system experiments. A reaction time that is too short, such as less than 60 minutes, will result in CO3... 2- Incomplete removal or excessively long reaction times (e.g., exceeding 120 min) can lead to side reactions or changes in the physical state of the generated CaCO3 and CaS, thus reducing regeneration efficiency. A method of adding the waste alkali solution dropwise using lime slurry as the base solution is adopted, ensuring the dropwise addition time is controlled to within 1 / 3 of the total reaction time to guarantee uniform reaction. Attached Figure Description

[0018] Figure 1 This is a flow chart of the lime causticization regeneration process of the deodorization absorption liquid for dyeing and printing wastewater according to the present invention. Detailed Implementation

[0019] To facilitate understanding of the present invention, it will be described more fully and in detail below, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0020] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0021] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0022] The lime causticization regeneration process described in this invention is a continuous or intermittent industrial production process. The optimal process parameters determined based on laboratory tests are: temperature 25℃, lime dosage 100% of the theoretical amount, and reaction time 90 min.

[0023] The lime causticization regeneration process of the present invention has the following steps: Step (1): Pretreatment unit.

[0024] The alkaline absorption waste liquid to be regenerated is sent to the pretreatment unit. During pretreatment, a bag filter or centrifugal filter is selected according to the suspended solids content, with a filtration accuracy of ≤100 μm, to remove suspended solids and mechanical impurities, resulting in a clarified waste alkaline liquid. A pH meter and conductivity meter are installed in the pretreatment unit to monitor the basic properties of the waste alkaline liquid in real time.

[0025] Step (2): Causticization reaction unit.

[0026] The pretreated clarified waste alkaline solution is chemically reacted with calcium hydroxide in a causticizing reactor to produce calcium carbonate and calcium sulfide precipitates, while simultaneously regenerating sodium hydroxide. The causticizing reactor can be either a batch stirred tank reactor or a continuous reactor. When the causticizing reactor is a batch stirred tank reactor, it is equipped with a jacketed temperature control system, and the pH value is monitored online during the reaction. When the causticizing reactor is a continuous reactor, it is a three-stage series stirred tank reactor or a tubular reactor, controlling the residence time of the material in each stage reactor to be 20-40 minutes.

[0027] When clarifying waste alkali solution and calcium hydroxide undergo a chemical reaction in a causticizing reactor, the feeding method can be either countercurrent or cocurrent feeding to ensure thorough mixing of the waste alkali solution and lime slurry. Slowly adding the waste alkali solution to the lime slurry avoids localized pH drops that could lead to incomplete reaction.

[0028] The process control parameters are shown in the table below:

[0029] Theoretical dosage calculation: based on CO3 in the feed waste alkali solution 2- and S 2- Real-time concentration detection, calculated according to stoichiometry: .

[0030] In the formula: Calcium hydroxide dosage, kg / h; : Ion concentration in feed liquid, g / L; Feed flow rate, m 3 / h; Molar mass of calcium hydroxide, 74 g / mol.

[0031] Step (3): Sedimentation / centrifugation separation unit.

[0032] Solid-phase treatment: The separated CaCO3 3- CaS mixed precipitates can be further used for elemental sulfur recovery or as raw materials for building materials.

[0033] Step (4): Regenerated liquid preparation and reuse unit.

[0034] The separated regenerated liquid enters a mixing tank, where an appropriate amount of fresh NaOH or dilution water is added according to the reuse requirements. After being mixed to the target concentration, it is reused in the deodorization system. Reuse can be done directly or by blending. For direct reuse, the regenerated liquid is directly pumped to the front or rear alkaline scrubbing tower as absorbent. For blended reuse, the regenerated liquid is mixed with fresh NaOH solution in a specific ratio before use.

[0035] The quality indicators for reused regenerated liquid are as follows:

[0036] Example 1: As Figure 1 As shown, a lime causticization regeneration process for deodorizing absorbent liquid in dyeing and printing wastewater is described.

[0037] (1) Source and nature of wastewater: The source of the deodorization absorption liquid of the dyeing and printing wastewater to be regenerated is the waste liquid discharged from the front-end alkaline washing tower of the deodorization system of the hydrolysis acidification pool of a dyeing and printing industrial park.

[0038] Deodorizing absorbent liquid composition: pH: 13.81; S 2- Concentration: 61.01 g / L; CO3 2- Concentration: 68.10 g / L; OH - Concentration: 10.91 g / L.

[0039] (2) Process conditions: Reaction temperature: 25℃; Calcium hydroxide dosage: 100% of theoretical amount, based on n(Ca(OH)2)=n(CO3) 2- )+n(S 2- Calculation; reaction time: 90 min; stirring speed: 300 rpm; calcium hydroxide concentration: 10 wt%.

[0040] (3) Process steps: First, the waste liquid from the alkali washing tower is collected in a waste liquid collection tank and sent to the pretreatment unit for pretreatment. The pretreatment unit uses a bag filter to separate the solid and liquid of the waste liquid from the alkali washing tower to obtain a clarified waste alkali liquid. The filtration accuracy is controlled below 100 μm. 100% of the theoretical amount of calcium hydroxide is sent to an intermittent stirred reactor. Stirring is started and the speed is controlled at 300 rpm. The stirred reactor is adjusted to 25°C and kept at a constant temperature. Under stirring, the quantitative clarified waste alkali liquid after pretreatment is slowly added to the metered calcium hydroxide solution in a reverse addition manner. The addition time is controlled at 30 min. After the addition is completed, the reaction temperature is maintained at 25°C and the stirring speed is 300 rpm. The reaction is continued for 60 min. The pH value is monitored online during the reaction. After the reaction is completed, heating and stirring are stopped. The resulting mixture is separated and filtered by a centrifuge in sequence. Finally, calcium sulfide, calcium carbonate and a small amount of calcium hydroxide mixed waste residue and regenerated alkali absorption liquid are separated. The solid phase enters the sulfur recovery unit or is used as a building material raw material; the separated liquid phase is sodium hydroxide regenerated liquid, which is collected in a regenerated liquid storage tank and directly reused in the alkaline washing tower of the dyeing and printing wastewater deodorization system, or is reused in the alkaline washing tower after being supplemented with fresh alkaline solution to adjust the concentration.

[0041] (4) Experimental results: Components of the regenerated alkali absorption solution: pH: 14.21; OH- -Concentration: 27.71 g / L; CO3 2- Removal rate: 97.42%; S 2- Removal rate: 71.77%; Ca 2+ Residue: 30.94 mg / L; NaOH regeneration rate: 78.75%.

[0042] Example 2: Temperature parameter optimization comparison: With the lime dosage fixed at 100% of the theoretical amount and the reaction time at 60 min, the effect of different temperatures was investigated. Other operating procedures were the same as in Example 1.

[0043]

[0044] Conclusion: Regeneration effects similar to those at high temperatures can be achieved at room temperature (25℃), and CO3... 2- It has the highest removal rate and the lowest energy consumption.

[0045] Example 3: Comparison of Lime Dosage Optimization: With a fixed temperature of 25℃ and a reaction time of 60 min, the effect of different dosages was investigated. Other operating procedures were the same as in Example 1.

[0046]

[0047] Conclusion: The highest NaOH regeneration rate was achieved at 100% of the theoretical dosage, and Ca... 2+ Minimal residue; excessive addition actually reduces regeneration rate and increases Ca. 2+ Residue.

[0048] Example 4: Comparison of Optimized Reaction Time: With a fixed temperature of 25℃ and a dosage of 100% of the theoretical amount, the effect of different reaction times was investigated. Other operating procedures were the same as in Example 1.

[0049]

[0050] Conclusion: The optimal parameters were achieved when the reaction time was 90 min; longer reaction times resulted in a decrease in regeneration rate.

[0051] The above embodiments only illustrate one or more implementations of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of protection of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A lime causticizing regeneration process for deodorizing absorbent liquid in dyeing and printing wastewater, characterized in that, Includes the following steps: (1) The deodorization absorption liquid of the dyeing and printing wastewater to be regenerated is pretreated to remove suspended solids and mechanical impurities, and a clear waste alkali liquid is obtained. (2) The pretreated clarified waste alkaline solution is reacted with calcium hydroxide in a causticizing reactor to convert sodium carbonate into calcium carbonate precipitate and sulfide into calcium sulfide. (3) The mixture after the reaction in step (2) is subjected to solid-liquid separation; the solid phase obtained is mainly calcium carbonate and contains calcium sulfide. The solid phase is used for elemental sulfur recovery or as a building material raw material; the liquid phase obtained is sodium hydroxide regenerated liquid, which is reused in the dyeing and printing wastewater deodorization system or reused after adjusting the concentration.

2. The lime causticizing regeneration process for the deodorizing absorbent liquid of dyeing and printing wastewater according to claim 1, characterized in that, The deodorizing absorbent liquid for the dyeing and printing wastewater to be regenerated is a saturated absorbent liquid obtained by absorbing waste gas containing H2S and CO2 with NaOH solution.

3. The lime causticizing regeneration process for the deodorizing absorbent liquid of dyeing and printing wastewater according to claim 2, characterized in that, The saturated absorbent is in S 2- The calculated Na2S concentration is 130-170 g / L, with CO3... 2- The calculated Na2CO3 concentration is 80-130 g / L, with OH... - The calculated NaOH concentration is 10-30 g / L, and the pH value is 12.5-14.

0.

4. The lime causticizing regeneration process for the deodorizing absorbent liquid of dyeing and printing wastewater according to claim 3, characterized in that, The pretreatment steps include: using a bag filter or centrifugal filter to perform solid-liquid separation on the deodorizing absorbent of the dyeing and printing wastewater to be regenerated, with the filtration accuracy controlled below 100 μm; and during the pretreatment process, the pH value of the waste alkali solution is monitored in real time using a pH meter.

5. The lime causticizing regeneration process for the deodorizing absorbent liquid of dyeing and printing wastewater according to claim 4, characterized in that, In step (2), when the clarified waste alkaline solution and calcium hydroxide react in the causticizing reactor, the reaction temperature is controlled at 15-35℃, the amount of calcium hydroxide added is controlled at 100%-110% of the theoretical amount of lime causticizing reaction, and the reaction time is controlled at 60-90 min.

6. The lime causticizing regeneration process for the deodorizing absorbent liquid of dyeing and printing wastewater according to claim 5, characterized in that, In step (2), when the clarified waste alkaline solution and calcium hydroxide react in the causticizing reactor, the reaction temperature is controlled at 25±2℃, the amount of calcium hydroxide added is controlled at 100% of the theoretical amount of lime causticizing reaction, and the reaction time is controlled at 90 min.

7. The lime causticizing regeneration process for the deodorizing absorbent liquid of dyeing and printing wastewater according to claim 6, characterized in that, When the clarified waste alkaline solution and calcium hydroxide react in the causticizing reactor, the clarified waste alkaline solution is added dropwise to the calcium hydroxide base solution, with calcium hydroxide as the base solution.

8. The lime causticizing regeneration process for the deodorizing absorbent liquid of dyeing and printing wastewater according to claim 7, characterized in that, The addition is carried out in a reverse or co-current manner, and the addition time of the clarified waste alkali solution is controlled to be within 1 / 3 of the total reaction time.

9. The lime causticizing regeneration process for the deodorizing absorbent liquid of dyeing and printing wastewater according to claim 8, characterized in that, The causticizing reactor is either a batch stirred reactor or a continuous reactor. When the causticizing reactor is a batch stirred reactor, it is equipped with a jacketed temperature control system, and the pH value is monitored online during the reaction. When the causticizing reactor is a continuous reactor, it is a three-stage series stirred reactor or tubular reactor, and the residence time of the material in a single-stage reactor is controlled to be 20-40 min.

10. The lime causticizing regeneration process for the deodorizing absorbent liquid of dyeing and printing wastewater according to claim 9, characterized in that, The process also includes an automated control step: based on real-time monitoring of the pH value and conductivity of the waste alkali solution using a pH meter and conductivity meter, and by using the waste alkali solution composition data measured by an online ion concentration analyzer, the theoretical requirement for calcium hydroxide is automatically calculated and precisely added using a variable frequency metering pump.

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